This invention relates generally to machines adapted to test material wear and lubrication properties. More specifically, the invention relates to loading mechanisms for such machines such as of the type having wear specimens disposed on either side of a rotating pin, the loading mechanism being adapted to apply pressure between the wear specimens and the pin for wear and lubrication testing purposes.
One such test machine is disclosed in M. Cornell, U.S. Pat. No. 2,110,288, and certain associated test methods are disclosed in F. A. Faville, U.S. Pat. No. 2,106,170 and F. A. Faville, U.S. Pat. No. 3,190,109. Standardized tests for such machines are included in ASTM D 2670-88, Measuring Wear Properties of Fluid Lubricants; ASTM D 3233-93, Measurement of Extreme Pressure Properties of Fluid Lubricants; and ASTM D 2625-90, Endurance (Wear) Life and Load-Carrying Capacity of Solid Film Lubricants.
In conventional prior machines of this general type, loading jaws (a.k.a. bearing block holders) located on either side of the pin carry wear specimens (a.k.a. bearing blocks) formed with a V-shaped notches for receiving and establishing bearing contact with the pin. During testing, a loading or force application mechanism moves the jaws inwardly toward the pin to establish a desired contact loading or pressure condition between the bearing blocks and the rotating pin.
In such prior machines, an operator manually adjusts a ratcheting loading mechanism to move the jaws into contact with the pin and establish the desired loading condition. The pressure between the bearing blocks and the pin is related to the position of the jaws and the ratchet mechanism, therefore, the pressure between the pin and the bearing blocks decreases as wear occurs. Maintaining a relatively constant bearing pressure requires constant vigilance by the test operator, and adjustment of the ratchet mechanism during the test, typically requiring several adjustments during a 60 second test (see e.g., Faville, U.S. Pat. No. 3,190,109, col. 4, lines 22-26). As a result, pressure loading conditions can vary substantially during a test, depending on the amount of wear and the operator's vigilance in watching for and correcting for changes in pressure due to the wear. Prior ratchet mechanisms of this type are also typically adapted for conducting a test under increasing loading conditions, however, the construction of such prior mechanisms, including relatively high hysteresis, generally preclude accurate, consistent, or controlled decrease of loading pressure during the same test and depending on the starting point of the increasing load in the hysteresis curve, can result in unrepeatable test results. In addition, such prior machines are not easily adapted for, and generally do not provide for measurement of wear during the test. These unfortunate characteristics and deficiencies of prior machines of this type are well known and documented in the prior art.